Show javac warnings for unknown enum constants

CompilerWarningsDemo.java

Path lib = Path.of("lib");

void main() throws Exception {
    step("Populate lib directory");
    var guardian = get("org.apiguardian.api", "https://repo.maven.apache.org/maven2/org/apiguardian/apiguardian-api/1.1.2/apiguardian-api-1.1.2.jar");
    var jspecify = get("org.jspecify", "https://repo.maven.apache.org/maven2/org/jspecify/jspecify/1.0.0/jspecify-1.0.0.jar");
    var commons = get("org.junit.platform.commons", "https://repo.maven.apache.org/maven2/org/junit/platform/junit-platform-commons/6.0.1/junit-platform-commons-6.0.1.jar");

    step("Describe module org.junit.platform.commons");
    run("jar", "--describe-module", "--file", commons);

    var program = Path.of("HelloCommons.java");
    if (!Files.exists(program)) {
        step("Create compact HelloCommons.java program");
        Files.writeString(program,
                """
                import module org.junit.platform.commons;
                
                void main() {
                  IO.println(getClass().getModule());
                }
                """);
    }

    var modular = Path.of("mod", "foo", "Modular.java");
    if (!Files.exists(modular)) {
        step("Create modular Modular.java program and module descriptor");
        Files.createDirectories(modular.getParent());
        Files.writeString(Path.of("mod", "module-info.java"),
                """
                module foo {
                  requires org.junit.platform.commons;
                }
                """);
        Files.writeString(modular,
                """
                package foo;
                
                import module org.junit.platform.commons;
                
                class Modular {
                  void main() {
                    IO.println(getClass().getModule());
                  }
                }
                """);
    }

    step("Run with all modules in play");
    listModules();
    run("java", "--module-path", "lib", "--add-modules", "ALL-MODULE-PATH", program);
    run("java", "--module-path", "lib", "--add-modules", "ALL-MODULE-PATH", modular);

    step("Run without JSpecify module");
    Files.deleteIfExists(jspecify);
    listModules();
    run("java", "--module-path", "lib", "--add-modules", "ALL-MODULE-PATH", program);
    run("java", "--module-path", "lib", "--add-modules", "ALL-MODULE-PATH", modular);

    step("Run without JSpecify and without API Guardian module");
    Files.deleteIfExists(guardian);
    listModules();
    run("java", "--module-path", "lib", "--add-modules", "ALL-MODULE-PATH", program);
    run("java", "--module-path", "lib", "--add-modules", "ALL-MODULE-PATH", modular);
}

void step(String caption) {
    IO.println();
    IO.println("### " + caption);
    IO.println();
}

Path get(String module, String uri) throws Exception {
    Files.createDirectories(lib);
    var target = lib.resolve(module + ".jar");
    var source = URI.create(uri);
    try (var stream = source.toURL().openStream()) {
        IO.println(module + " <- " + source + "...");
        Files.copy(stream, target, StandardCopyOption.REPLACE_EXISTING);
    }
    return target;
}

void listModules() {
    var finder = ModuleFinder.of(lib);
    var modules = finder.findAll();
    modules.stream()
            .map(ModuleReference::descriptor)
            .map(ModuleDescriptor::toNameAndVersion)
            .sorted()
            .forEach(IO::println);
    var size = modules.size();
    IO.println("    %d module%s".formatted(size, size == 1 ? "" : "s"));
}

void run(String tool, Object... args) throws Exception {
    var program = Path.of(System.getProperty("java.home", ""), "bin", tool);
    var builder = new ProcessBuilder(program.toString()).inheritIO();
    builder.command().addAll(Stream.of(args).map(Object::toString).toList());
    IO.println("| " + String.join(" ", builder.command()));
    var process = builder.start();
    var code = process.waitFor();
    if (code == 0) return;
    throw new Error(tool + " returned a non-zero exit code: " + code);
}

log.txt

### Run with all modules in play

org.apiguardian.api@1.1.2
org.jspecify
org.junit.platform.commons@6.0.1
    3 modules
| J:\jdks\jdk-25\bin\java --module-path lib --add-modules ALL-MODULE-PATH HelloCommons.java
unnamed module @10b48321
| J:\jdks\jdk-25\bin\java --module-path lib --add-modules ALL-MODULE-PATH mod\foo\Modular.java
module foo

### Run without JSpecify module

org.apiguardian.api@1.1.2
org.junit.platform.commons@6.0.1
    2 modules
| J:\jdks\jdk-25\bin\java --module-path lib --add-modules ALL-MODULE-PATH HelloCommons.java
unnamed module @7fad8c79
| J:\jdks\jdk-25\bin\java --module-path lib --add-modules ALL-MODULE-PATH mod\foo\Modular.java
error: module not found: org.jspecify
1 error
error: compilation failed
Exception in thread "main" java.lang.Error: java returned a non-zero exit code: 1
        at CompilerWarningsDemo.run(CompilerWarningsDemo.java:104)
        at CompilerWarningsDemo.main(CompilerWarningsDemo.java:58